1. Field of the Invention
The present invention relates to a uretedione derivative, more particularly to a uretedione derivative for aqueous-based polyurethane.
2. Description of the Related Art
Polyurethanes are a type of polymers that can have widely differing properties. Such versatility and multitude properties permit some of the polyurethanes to exhibit an elasticity and a flexibility similar to those of rubbers, and others to exhibit a mechanical strength and a hardness similar to those of plastics. As such, polyurethanes are wildly used in the manufacture of products, such as shoesoles, synthetic leathers, adhesives, sealants, printing inks, foams, films, coatings, and fiber modifiers.
Applications of solvent-based polyurethanes and technologies for the process of producing the same are well developed. However, due to problems with respect to the environment, economy, sanitation, and safety, the solvent-based polyurethane tends to be gradually replaced by aqueous-based polyurethane which is an environmental friendly product that dispenses with the use of the solvent.
While there has been a great demand for aqueous-based polyurethane, the physical and mechanical properties of the same are still insufficient in comparison with those of the solvent-based polyurethane. Difficulties have been encountered for current technologies for producing aqueous-based polyurethane in enhancing the molecular weight and the cross-linking density of the polyurethane. Such properties are often improved by post-curing reaction which unfortunately results in limiting the applications of the aqueous-based polyurethane.
There are several types of self-emulsifiable aqueous-based polyurethane available in the market. These aqueous-based polyurethanes can be classified into non-ionic, cationic, and anionic aqueous-based polyurethanes depending on the nature of the hydrophilic group of the polyurethane. For instance, when dissolved in water, the carboxy groups of the anionic aqueous-based polyurethane provide surface charges to the surrounding of the polyurethane molecules (particles), thereby causing repulsion between the polyurethane molecules (particles) and resulting in uniform distribution of the polyurethane molecules in the water phase. Such behavior permits the aqueous-based polyurethane to form into a polyurethane emulsion upon mixing with water, and is similar to a surfactant which acts as an emulsifier and which is formed into a plurality of micro-cells in a water phase. Because of the hydrophilic property of the carboxy group, the polyurethane becomes self-emulsifiable or water-reducible in the water phase. Such aqueous-based polyurethanes have a common disadvantage similar to that of a polymeric surfactant in that, after drying into a film, such film exhibits a high water absorptivity.
As described in the publications, the improvements on aqueous-based polyurethane are normally performed by post-curing reaction to enhance the molecular weight and the cross-linking density of the polyurethane so as to broaden the applications of the same. Conventionally, such post-curing reaction is carried out by mixing "two components" together, i.e., adding a liquid containing the post-curing agent into another liquid containing the aqueous-based polyurethane before the application. However, such mixing of "two components" may result in instability to the quality of the polyurethane products due to the variations of the ratio of the "two components" and the degree of the uniformity of the agitation. The occurrence of such instability is particularly severe in a batch process, and can significantly restrict the applications of the aqueous-based polyurethane.
In the case of the process for producing anionic (carboxy group) polyurethane emulsion, the addition of water into an isocyanate-terminated urethane prepolymer is an essential step to form the polyurethane emulsion. The formation of the anionic carboxy group polyurethane emulsion is better described from the following scheme: ##STR1##
As described in the above reaction scheme, isocyanate-terminated urethane prepolymer is prepared by reacting isophorone diisocyanate with polypropylene glycol in the presence of dimethylpropionic acid. The terminal isocyanate groups of the thus formed urethane prepolymer are hydrolyzed to amino groups by water. The amino groups of the urethane prepolymer may result in a self-chain extending reaction by reacting with the isocyanate groups of the urethane prepolymer to form urea bonding, or may be present in the water phase without further reaction. While the presence of the amino groups and the carboxy groups of the aqueous-based polyurethane can stabilize the polyurethane emulsion, they also result in high water absorptivity which significantly affects the subsequent processing of the polyurethane emulsion, such as dyeing.